3D printing, also known as additive manufacturing, is a revolutionary method of producing 3-dimensional objects by accumulating successive layers to form the final products. Similar to an inkjet printer which prints words and patterns on paper or other surfaces by propelling droplets of ink onto them, a 3D printer has a extruder to eject droplets of printing materials of which the most common one is plastic. The distinction is that  rather than line after line it prints layer on layer, which means the final product will have not only width and length, but also height. To do this, the extruder of a 3D printer can move 3-dimensionally. A plastic thread is connected to the top of the printing module, which is fixed on two rails, then it is melt in a heater within the module and turned into droplets. The extruder at the bottom of the module then propels them onto the plate, making a layer of plastic. After that, the extruder moves a tiny distance up and prints another layer. The process goes on and on and finally we can have a 3D product.